最新3nucleotidessynthsis汇总

are both inhibited by the end products IMP, AMP and GMP (AMP and GMP act synergistically). AMP inhibits adenylosuccinate synthetase and GMP inhibits IMP dehydrogenase. AMP and GMP synthesis is balanced by the following mechanism: GTP is needed for AMP synthesis and ATP for GMP synthesis.
Salvage pathways recycle the free bases and nucleosides released from nucleic acid breakdown.
The free bases are not intermediates during the de novo synthesis
Radioisotope tracer experiments revealed the origins of the ring atoms of purines
Gln amቤተ መጻሕፍቲ ባይዱde
C
HCO3-
The atoms of the pyrimidine rings are derived from HCO3-, Gln and Asp.
The de novo synthesis of AMP and GMP is regulated mainly by sequential feedback Inhibition.
Summary
The first intermediate to have a complete purine ring is IMP (inosinate次黄嘌呤单核苷酸).
• Steps 1, 3, and 5; steps 7 and 8 ;steps 10 and 11 are catalyzed by a multifunctional protein respectively in some eukaryotic cells.
• In bacteria, these activities are found on separate proteins, but a large noncovalent complex may exist in these cells.
1. De novo purine nucleotide synthesis begins with PRPP
PRPP is synthesized from ribose 5-P in a Reaction catalyzed by PRPP synthetase.
The bases are not synthesized and then attached to ribose
amidotransferase
The biosynthesis of AMP and GMP is regulated by feedback inhibition
Three major feedback mechanism cooperate PRPP synthetase and glutamine-PRPP amidotransferase
3nucleotidessynthsis
Overview
Two types of pathway lead to nucleotides
De novo synthesis of nucleotides begins with their metabolic precursors: amino acids, ribose 5-phosphate, NH3, and CO2.
The deoxyribonucleotides (dNDPs) are synthesized by reduction of ribonucleotides (NDPs).
The origin of the atoms in the purine and pyrimidine rings
Radioisotope tracer experiments revealed the origin of the atoms in the purine and pyrimidine rings Buchanan and Greenberg did this by feeding a variety of isotopically labeled compounds to pigeons (1940s). The atoms of the purine rings were found to be derived from formate, CO2, Gly, Asp, and Gln. The atoms of the pyrimidine rings were found to be derived from Asp, Gln and HCO3-.
The purine ring is assembled on ribose phosphate to make AMP and GMP; the pyrimidine ring is first synthesized as orotate, which is then attached to ribose phosphate before being converted to UTP and CTP (dTMP is made from dUMP).
The purine ring is built up one or a few atoms at a time, attached to ribose throughout the process.
The enzymes of IMP synthesis appear to be organized as large multienzyme complexes